This invention relates to a magnetic bearing system in which there is relative rotation between first and second members, one of which carries a plurality of electrically conductive loops, and the other of which is provided with field magnets which produce magnetic fields to which the loops are subjected. When the relative rotation is such that the loops travel in a prescribed circular path for which they were designed, each loop is subjected to zero net magnetic flux so no electrical current flows through the loops. However, when the path of the loops deviates from the prescribed path, each loop will be subjected to a finite net magnetic flux to produce electromotive forces in the loops. This will induce an electrical current in the loops, the direction of which, in the presence of the magnetic fields, will exert Lorentz forces on the loops and their respective member in a direction which is lateral with respect to the circular path. The lateral direction is radial in a radial bearing, and it is axial in an axial bearing. Such magnetic bearings systems are the subject of U.S. Pat. No. 5,305,874 described above, which is incorporated herein by reference.
It has been discovered that a magnetic bearing of the foregoing type, when subjected to gravitational or other forces, will respond with a force pulses of an alternating nature so that forces are sequentially exerted in opposite directions. If the frequency of these forces is near or equal to a natural frequency of the entire rotor assembly, a mechanical resonance condition may result and the bearing may be damaged or destroyed.
The present invention provides a novel magnetic bearing system which will minimize force fluctuations and provide increased stability over a range of rotational speeds, and it will avoid any risk of vibratory damage brought about by the force pulses as described above.